1. Field of the Invention
The present invention relates to a line terminating device for terminating subscriber lines accommodated in an ATM exchange. More particularly, it relates to a line terminating device, which terminates different lines in a synchronous optical network (hereinafter, it called as SONET) and a synchronous digital hierarchy (hereinafter, it called as SDH) network.
FIG. 8 shows a general system structure of an ATM exchange, in which SONET/SDH lines are accommodated. In FIG. 8, the ATM exchange contains line terminating devices 10, each of which has function of interfacing lines, and an ATM self-routing switch 20.
The line terminating device 10 interfaces the ATM switch 20 with either an OC3C/STM-1 optical transmission path having a speed of 155.52 Mbps or an OC12C/STM-4 optical transmission path having a speed of 622.08 Mbps.
In here, a frame format of a signal flowing to the OC3C/STM-1optical transmission path having the speed of 155.52 Mbps is shown in FIG. 9A. The frame format has a frame size of 9 bytes xc3x97270 bytes, and therefore, data of total 2,430 bytes is transmitted with 125 xcexcs.
On the other hand, a frame format of a signal flowing to the OC12C/STM-4 optical transmission path having the speed of 622.08 Mbps is shown in FIG. 9B. The frame format has the same frame size as the fourth times of that of the signal shown in FIG. 9A. In other words, the frame format shown in FIG. 9B has the frame size of 9 bytesxc3x971,080 bytes, and therefore, data of the total 9,720 bytes is transmitted with 125 xcexcs.
Additionally, both of the above-described frame formats have areas for alarming or quality management, which are so called section over head (SOH), line over head (LOH) and path over head (POH). On the other hand, a payload section is actually used as a data area to map an ATM cell and the like.
The line terminating device 10 is required to process signals of the above-described frame formats having different line speeds. Accordingly, the conventional line terminating device 10 of the ATM exchange is constituted so as that a peculiar physical layer terminating section is provided corresponding to each transmission speed, as shown in FIGS. 10A and 10B.
FIG. 10A illustrates an example of the conventional hardware structure, in which a hardware 200a for processing a signal of 155.52 Mbps and the corresponding physical layer terminating section 100a connected to the line of the speed of 155.52 Mbps are provided. On the other hand, FIG. 10B illustrates an example of the conventional hardware structure, in which a hardware 200b for processing a signal of 622.08 Mbps and the corresponding physical layer terminating section 100b connected to the line of the speed of 622.08 Mbps are provided.
Therefore, it has been considered that independent hardware devices 200a and 200b should be prepared respectively for different line speeds in the conventional ATM exchange system. A line speed of the transmission path accommodated in an ATM exchange depends on how to construct a transmission system.
In the conventional ATM exchange system, assuming a general combination of the line speeds, correspondingly hardware devices 200a and 200b for signal processing are provided to constitute a line terminating device.
That brings a problem such that a circuit scale becomes large because one circuit is required for one line speed, and therefore, plural circuits are required for different line speeds. Additionally,different firmware for controlling each circuit structure should be prepared independently. That brings another problem such that the cost and the manufacturing steps are increased when developing an ATM exchange system.
Accordingly, it is an object of the present invention to provide a line terminating device to solve the above-described conventional problems.
It is another object of the present invention to provide a line terminating device, which terminates lines, each having a different line speed, in SONET/SDH networks, to reduce a scale of the circuit, the number of external terminals, the number of steps of developing a firmware, and a scale of the firmware.
The above-described objects of the present invention can be achieved by a line terminating device, which terminates plural SONET/SDH lines, including a main signal processor where clock and data lines are commonly used, and a selector for selecting one of the plural SONET/SDH lines.
The main signal processor processes the data of the selected one of the plural SONET/SDH lines, which is switched and output by the selector, according to a clock signal corresponding to the selected line speed.
In one preferred mode of the present invention, the clock signal corresponding to the line speed switched and output by the selector is switched and output from the plural clock signals corresponding to each of the plural SONET/SDH lines, which is generated from one oscillating source.
Alternatively, in other preferred mode of the present invention, the main signal processor extracts an over head of the data of the line output from the selector according to a clock signal corresponding to the line speed of the line switched and output from the selector, and further includes an interface section having an area for storing monitored information in the extracted overhead in each address corresponding to the status of the monitored information, and a firmware for collecting the monitored information stored in the interface section.
Further, other objects of the present invention will become clear by the description for explaining embodiments according to the attached drawings.